Jax can still be affected by crowd control effects while using Leap Strike.

Jax can still use abilities and spells while jumping with Leap Strike.

Leap Strike can be used to jump over terrain, provided that there is enough room for Jax on the other side.

Damage is dealt whether Jax jumps to his target or not, as long as the target was in range upon cast.

Leap Strike can be used on wards, temporarily revealing it for 2 seconds afterwards.

Leap Strike can sometimes appear to be able to be cast on something that appears to be outside of the ability's range, most notably, wards placed over terrain. Examples can be seen in this video demonstration.

Empower

(Active): Jax charges his weapon with energy, causing his next autoattack or Leap Strike to deal additional magic damage. This ability resets the autoattack timer.

The buff granted by Empower will not be consumed on attacking structures such as turrets. However Jax can still use the ability to reset his autoattack timer (and therefore do more damage to the structure).

If Jax uses Leap Strike while buffed by Empower, the buff will proc and be consumed to deal the bonus magic damage.

Counter Strike

(Active): Jax enters a defensive stance for up to 2 seconds, dodging all incoming basic attacks and taking 25% less damage from area of effect abilities. At the end of the duration or if Counter Strike is activated again, Jax deals physical damage and stuns nearby enemies for 1 second. This spell deals 20% additional damage for each attack dodged to a maximum of 100% increased damage.

Counter Strike is a self-target ability that grants Jax a buff, allowing him to dodge all incoming autoattacks and reducing damage taken from area of effect abilities by 25%. After 2 seconds or when Counter Strike is activated again, Jax deals physical damage and stuns enemy units in a radius around him.

Activating Grandmaster's Might has no cast time and does not interrupt Jax's previous orders.

Grandmaster's Might only calculates the bonus armor and magic resist once, at the moment the ability is cast. Changes to his stats while Grandmaster's Might is active will not cause the bonus to adjust.